In research and development of structural materials and, in particular, the National Aeronautics and Space Administration, directional solidification experiments that are part of the planned materials processing in space (MPS) program for the manned Space Shuttle during the next few years, are the process steps involving insertion into and retrieval from a high temmperature furnace of a fused quartz ampoule. These fused quartz ampoules are used to house material samples subject to thermal cycling from 20.degree. C. to temperatures exceeding +1000.degree. C. Presently, high temperature resistant adhesive cements are utilized to attach the fused quartz ampoules to the metal insertion-retrieval mechanism. Adhesives that can withstand the extreme temperatures contemplated for use with the present technique would likely be of a ceramic origin and brittle. Thus, failure of the adhesive connection may occur due to the different coefficients of thermal expansion between the fused quartz and the metal insertion-retrieval rod. Also, cemented objects may not be reusable, leading to higher costs and creating additional problems after each thermal cycling test.
Also, fused quartz to metal seals have been employed by fusing various transition materials such as Kovar and Pyrex between the metal holder and the fused quartz and molybdenum to quartz seals can be made without the use of a transition layer. Holders made with a transition material, as well as clamps employing O-ring type connections have a limited temperature capability and are thus not suitable in the temperature cycling tests contemplated by the present invention. The molybdenum to fused quartz seals are not temperature limited, but their formation involves a highly specialized process and is of limited availability. Each of these prior art systems require construction of a new holding mechanism for each test operation.
It is therefore an object of the present invention to provide a reusable novel connection or clamp mechanism between objects adapted to be subjected to thermal cycling.
Another object of the present invention is a novel reusable clamp for connecting two objects.
A further object of the present invention is to provide a clamp connection for two objects that will maintain a snug connection therebetween throughout the temperature cycle of 20.degree. C. to 1000.degree. C. and without danger of rupturing fragile test objects.
An additional object of the present invention is a method for releasably connecting a fused quartz object to a thermal cycling resistance insertion tool.
A further object of the present invention is a clamp mechanism for a thermal cycling test object that will maintain constant pressure on the test object during a temperature cycle.
Another object of the present invention is to provide a reusable retention mechanism for insertion and withdrawal of a fused quartz object relative to a high temperature environment.
According to the present invention the foregoing and additional objects are attained by providing a reusable clamp device integrally attached to or formed with a temperature resistant metal insertion/retrieval rod or sting device and adapted to releasably retain a test fused quartz ampoule. The reusable clamp device is in the form of a sleeve having a first end portion integral with the metal rod and a second end portion being a plurality of circumferentially disposed spaced fingers extending from and along the longitudinal axis of the first end portion. At least a portion of the spaced fingers are provided with circumferentional exterior threads to receive a threaded lock nut or collar thereon. As the lock nut is tightened, a squeezing or inwardly biasing force is exerted on the fingers to cause a clamping force to be exerted on the portion of the fused quartz ampoule positioned within the fingers. A compressible seal or packing is provided between the quartz ampoule and the fingers. This compressible seal is selected from a material which has an anisotropic thermal expansion coefficient with negligible expansion in the plane of the quartz rod walls but a relatively large coefficient of expansion in the radial direction to thereby maintain a snug fit between the fused quartz material and the clamp when temperature cycled between 20.degree. C. and 1000.degree. C.